Mask



FIG. 1 is a front elevational view of a mask, showing my new design;

FIG. 2 is the rear elevational view thereof;

FIG. 3 is the left side view thereof;

FIG. 4 is the right side view thereof;

FIG. 5 is the top plan view thereof; and,

FIG. 6 is the bottom view thereof. 

The ornamental design for a mask, as shown and described. 